The present invention generally relates to the art of chemical mechanical polishing for use in fabrication of semiconductor devices and more particularly to a polishing cloth for use in a chemical mechanical polishing process, including a surface treatment thereof.
With recent progress in the fabrication of very large scale integrated circuits, the number of devices included in an integrated circuit is increasing. Associated therewith, the degree of complexity of interconnection patterns used in an integrated circuit for interconnecting various devices is also increasing. In order to realize such complex interconnection patterns, recent advanced integrated circuits tend to use so-called multilayer interconnection structure, in which the interconnection pattern is provided in a plurality of layers, with intervening interlayer insulation films.
On the other hand, such a multilayer interconnection structure tends to cause a problem of increased step height on an interlayer insulation film covering an underlying interconnection pattern. Due to the increased step height, there is a substantial risk that an interconnection pattern provided above interlayer insulation film may experience distortion or disconnection. Further, such an irregularity at the top surface of the interlayer insulation film tends to cause a problem of poor patterning of the interconnection pattern due to the limited focal depth of the high-resolution optical system used for exposing such extremely miniaturized interconnection patterns. This problem becomes particularly acute in recent advanced integrated circuits having a very large integration density.
Thus, planarization is a paramount problem in realizing a multilayer interconnection structure, and various investigations have being undertaken for overcoming this problem.
Conventionally, the planarization has been conducted by providing the interlayer insulation film as a low-viscosity material such as an SOG (spin-on-glass) or a low melting silicate glass containing B or P. However, such a conventional planarization process becomes less effective in CMOS devices having a design rule of 0.35 .mu.m or less, in which a further degree of planarization is required for the entire wafer surface.
The art of chemical mechanical polishing referred to hereinafter as CMP is a technology that can meet such a stringent demand. By using a CMP process, it is possible to planarize a wafer substantially completely and eliminate projections or depressions from the surface of the wafer.
FIG.1 shows the construction of a polishing apparatus for use in a CMP process of a semiconductor substrate.
Referring to FIG. 1, the polishing apparatus includes a rotary disk or platen 10 covered by a polishing cloth 12. Further, a rotary polishing head 14 is provided on the platen 10 so as to face the top surface of the platen 10 covered by the polishing cloth 12. The polishing head 14 holds thereon a substrate 16 to be polished, and there is provided a slurry nozzle 20 above the platen 10 such that the slurry nozzle 20 drops a slurry 18 on the polishing cloth 12.
In operation, the platen 10 and the polishing head 14 are driven at respective predetermined speeds while the slurry is dripped on the polishing cloth 12, and the polishing head 14 urges the substrate 16 against the polishing cloth 12 with a predetermined urging force or pressure. Conventionally, a slurry in which alumina or colloidal silica abrasives are dispersed in an alkaline solvent has been used for the slurry 18. Further, a foamed polymer such as a polyurethane sheet has been used for the polishing cloth 12.
In such a CMP process conducted by the polishing apparatus of FIG.1, it should be noted that the surface state of the polishing cloth 12 provides a profound influence on the mechanism of polishing, including retention of the slurry 18 thereon. Thus, in order to achieve an optimized polishing, it is necessary to control the surface state of the polishing cloth 12.
In the conventional polishing cloth 12, the surface of the cloth 12 includes minute projections and depressions that are formed merely by chance by a foaming process that occurs at the time of manufacturing the polishing cloth 12. In other words, the surface state of the conventional polishing cloth 12 is controlled merely by chance. Thus, the conventional CMP process conducted by using such a conventional polishing cloth 12 is difficult to be optimized, and there has been difficulty in polishing the substrate 16 with a constant polishing rate and with reproducibility.
There are polishing cloths that include grooves or minute depressions for holding the slurry. However, the size of the grooves or depressions in such conventional polishing cloths is on the order of millimeters, while such large depressions are not effective for improving the polishing process.
In order to be effective, the grooves on the polishing cloth should have a size range of microns. At the same time, there has been no effective means for forming such minute grooves in the polishing cloth. While there is a proposal to grind the surface of the polishing cloth by a tool that carries thereon electrodeposited diamond abrasives such that grooves of micron size are formed on the surface of the polishing cloth, there has no investigation as to what process should be the optimum.
After a continuous use, the polishing cloth tends to collect particles that are formed as a result of the polishing. The particles may include worn out abrasives. In conventional polishing cloths, it has been difficult to remove such particles without affecting the performance of the polishing cloth.